Debris screen for a downhole tool

ABSTRACT

A debris screen, sealingly and releasably latched to the top of a polished bore of a downhole tool for preventing the ingress of debris into the polished bore. Typically the debris screen is connected to a tieback receptacle of a liner hanger assembly. The debris screen is connected to a setting tool and is axially moveable on the setting tool permitting the setting tool to be stroked inside the liner hanger assembly during normal operations, such as cementing while retaining the debris screen at the top of the tieback receptacle at all times except during the final stages of retrieval. The debris screen has a tubular sleeve having a plurality of ports, covered by a wedge wire screen through which fluids can flow. Further, the latching mechanism has a plurality of ports to permit the flow of debris-free fluids from the wellbore into the annulus between the setting tool and the downhole tool.

FIELD OF THE INVENTION

[0001] The invention relates to tools for running in and settingdownhole tools and particularly to debris barriers for liner hangerrunning tools.

BACKGROUND OF THE INVENTION

[0002] Typically, liner hanger systems comprise a liner hanger fromwhich a liner is suspended and which is lowered into a wellbore using arunning tool connected at the end of a tubing string. The running toolis releasably connected to the liner hanger for retrieval once the linerhas been cemented into place. A tieback receptacle having a polishedbore is connected at a top end of the liner hanger to provide a surfaceagainst which seals can be applied in order to actuate other downholeequipment such as packers and the like.

[0003] During running in of the liner hanger and during normaloperations required to set the slips of the liner hanger, debris mayenter the annulus between the running tool and the tieback receptacle,particularly when the running tool is stroked up and down during normalsetting operations. Debris which becomes trapped in the annulus maycause the running tool to become stuck, necessitating an expensivefishing expedition to retrieve it to surface. Further. debris may damagethe polished bore as the running tool is stroked up and down, resultingin damage that affects the ability of seals to seal against the bore.

[0004] It is known in the industry to use a debris barrier to preventdebris from entering the polished bore of the tieback receptacle. Mostdebris barriers block the passage of debris and are fixed to the mandrelof the running tool such that as long as the running tool remains in thetieback receptacle, debris is excluded from entering the annulus,however, once the running tool is lifted, the annulus is exposed anddebris may enter.

[0005] Other debris barriers are connected to the upper end of thetieback or similar receptacle and are axially moveable on the mandrel ofthe running tool to maintain the debris barrier at the top of thetieback receptacle during all normal operations, except retrieval.

[0006] U.S. Pat. No. 6,065,536 to Gudmestad teaches a debris barrier orjunk bonnet comprising a pair of seals, one between a tubular member andthe junk bonnet and the second between the junk bonnet and the polishedbore. The junk bonnet slideably engages the outer wall of the tubularmember and extends to the polished bore to provide a physical barrieragainst debris entering the polished bore. The junk bonnet is held atthe top of the polished bore by dogs which engage a groove in thepolished bore. The junk bonnet is restrained from rotation. As thetubular member is lifted to remove the attached running tool a shear pinis sheared and the dogs retract to release the junk bonnet and therunning tool. With the exception of fluid which can flow past the seals,fluid flow through the junk bonnet is not contemplated. Further, shoulddebris pack about the top of the junk bonnet there is a danger of ahydraulic lock forming which may restrict the axial motion of therunning tool and the junk bonnet thereon.

[0007] U.S. Pat. No. 5,582,253 to Fraser teaches a plurality of ringsand a collet system to latch a tool mandrel to a setting sleeve having apolished bore. One of said plurality of rings effectively covers theannular space between the mandrel and the sleeve providing a physicalbarrier to debris at the top of the polished bore. Fraser relies on aclose tolerance between the ring and the mandrel to exclude debris whileacting as a “leaky seal” to prevent pressure trapping on one side of thesetting sleeve. Should debris pack about the top of the ring, theadvantage of the leaky seal may be overcome and pressure trapping couldoccur. The apparatus of Fraser offers no alternate pressure relief.

[0008] Baker Oil Tools unit No. 4664 Liner Top Debris Barrier found inthe Baker Oil Tools catalogue provides a screen filter held in a housingand mounted at a top of the polished bore using a shear screw. Thepolished bore is drilled and tapped to allow the shear screw connectionand therefore, once the running tool is removed, remnants of the shearscrew and the hole created in the polished bore can create an impedimentfor seals to seal properly against the bore. Further, seals insertedpast the remaining protrusions may be damaged. A rupture disc isprovided below the screen to relieve pressure should the screen becomeplugged.

[0009] U.S. Pat. No. 5,628,366 to Telfer teaches a junk bonnet that ishydraulically locked into position in the polished bore without relianceon mechanical fastening. The junk bonnet comprises a complex sealingarrangement having uphole and downhole seals which create an annularvolume therebetween that is filled with hydraulic oil. The junk bonnetpermits normal operational movements of the downhole assembly whileretaining position at the top of the polished bore.

[0010] Clearly what is required is a simple, reusable debris barrierwhich permits the flow of fluids in an out of the annular space betweenthe running tool and the tieback receptacle during stroking of therunning tool in normal operation. The debris barrier must retainposition at the top of the tieback receptacle until such time as therunning tool is removed. Further, the debris barrier should preventpressure locking due to blockage by debris and should not damage theintegrity of the polished bore during insertion or removal therefrom.

SUMMARY OF THE INVENTION

[0011] In one aspect of the invention, a debris screen is providedpreventing the ingress of debris to a tool annulus between a settingtool inserted into a downhole tool in a wellbore and a polished bore ofthe downhole tool, the setting tool being axially moveable within thepolished bore. The debris screen comprises: a tubular sleeve formed overan exterior surface of the setting tool, and axially moveable thereon,defining a sleeve annulus therebetween, contiguous with the toolannulus, the sleeve having a plurality of ports formed therethrough forpermitting fluid communication between the sleeve annulus and thewellbore; a screen formed over the tubular sleeve for preventing thepassage of debris therethrough; a seal positioned at a top end of thetubular sleeve and extending between the tubular sleeve and the settingtool, the seal being sized so as to permit limited flow of fluidtherethrough for preventing pressure locking, while blocking debris; andmeans for latching the tubular sleeve sealingly to a top of the polishedbore and permitting fluid communication between the sleeve annulus andthe tool annulus.

[0012] Preferably, the means for latching is a latching mechanismoperable between the tubular sleeve and the polished bore wherein thelatching mechanism releasably engages an annular groove at a top of thepolished bore for retaining the tubular sleeve adjacent the top of thepolished bore and permitting axial movement of the setting tool therein.

[0013] More preferably, the latching mechanism comprises a plurality oflatch dogs housed within a latch dog housing, the latch dog housingbeing moveable between a downhole position and an uphole position. Inthe downhole position, the latch dog housing supports the latch dogs inan extended position wherein the latch dogs engage the groove on the topof the polished bore thus retaining the debris screen at the top of thepolished bore. In the uphole position the latch dog housing permits thelatch dogs to move to a retracted position wherein the latch dogs areretracted into the latch dog housing to release the latch dogs from thegroove, thus permitting retrieval of the tool and the debris screen.Movement of the latch dog housing from the downhole position to theuphole position is accomplished by lifting the setting tool until ashoulder at the bottom of the setting tool mates with a shoulder on thelatch dog housing. Lifting pressure applied to the setting toolovercomes shear screws, permitting the latch dog housing to move to theuphole position, the latch dogs to retract into the latch dog housingand retrieval of the debris screen and setting tool.

[0014] Alternatively, well suited for insertion into smaller diameterdownhole tools, the latching mechanism is a collet system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a partial longitudinal sectional view of a debris screenof the present invention, showing a cutaway portion attached to the topof a tieback receptacle's polished bore;

[0016]FIG. 2a is a longitudinal sectional view of a latched latchingmechanism according to FIG. 1 having a plurality of latch dogs actingbetween the debris screen and the polished bore, the latch dogs shown ina radially extended position;

[0017]FIG. 2b is a longitudinal sectional view of an un-latched latchingmechanism according to FIG. 1 having a plurality of latch dogs actingbetween the debris screen and the polished bore, the latch dogs shown ina retracted position;

[0018]FIG. 3a is a sectional view of a portion of a collet systemaccording to a second embodiment of the latching mechanism, showing acollet finger from an inside of the tubular housing;

[0019]FIG. 3b is a sectional view of the collet system according to FIG.3a, showing an inside of a collet retainer, having a plurality of portsformed at a lower edge;

[0020]FIG. 4a is a longitudinal sectional view of a latched latchingmechanism according to FIGS. 3a-3 b, having a collet system actingbetween the debris screen and the polished bore, the collet shown in adownhole engaged position; and

[0021]FIG. 4b is a longitudinal sectional view of an unlatched latchingmechanism according to FIGS. 3a-3 b having a collet system actingbetween the debris screen and the polished bore, the collet shown in anuphole non-engaged position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] Having reference to FIGS. 1-3, a debris screen 10 of the presentinvention is shown. The debris screen 10 comprises a tubular sleeve 11which is positioned about an outer surface of a setting tool 12 forminga sleeve annulus 13 therebetween. The tubular sleeve 11 is releasablylatched to a top end 14 of a downhole tool having a polished bore 15,such as a tieback receptacle attached to the top of a liner hangerassembly, to prevent the ingress of debris to a tool annulus 16 betweenthe setting tool 12 and the polished bore 15. The tubular sleeve 11 hasa plurality of ports 17 formed therethrough to provide fluidcommunication between the wellbore and the sleeve annulus 13, the sleeveannulus 13 being contiguous with the tool annulus 16. Means are providedfor flow A of fluids between the sleeve annulus 13 and the tool annulus16.

[0023] The setting tool 12 is axially moveable through the debris screen10. As the setting tool 12 is stroked up and down through the tubularsleeve 11 and within the polished bore 15, such as when reciprocatingthe setting tool 12 to ensure that the setting tool is released from theliner hanger assembly prior to cementing, fluid may be caused to flow Ain and out of the ports 17. A tubular wire screen 18, such as a wedgewire screen available from Variperm Canada Limited, Calgary, Alberta,Canada, is affixed over the tubular sleeve 11 to prevent debris fromentering the ports 17 with the fluid.

[0024] Means, such as a latching mechanism 30, maintains the debrisscreen 10 at the top 14 of the polished bore 15 except during the finalstages of retrieval of the setting tool 12 from the polished bore 15.Thus, the polished bore 15 is protected from damage resulting fromdebris being scratched along the polished bore during the axial movementof the setting tool 12 therein during routine operations.

[0025] Preferably, as shown in FIG. 1, an upper end 19 of the tubularsleeve 11 is connected to a top sub 20. The top sub 20 is formed havinga lower portion 22, an upper cap portion 22 and a pipe wiper 23sandwiched therebetween. The pipe wiper 23 acts as a “leaky seal” at theupper end 20 of the tubular sleeve 11, preventing debris from enteringthe annulus 13 between the tubular sleeve 11 and the setting tool 12,while allowing limited flow of fluids therethrough to prevent pressurelock should the screen 18 become plugged with debris.

[0026] In one embodiment of the invention, as shown in FIGS. 1, 2a-2 b,the latching mechanism 30 is located adjacent a lower end 33 of thetubular sleeve 11. The latching mechanism 30 comprises a plurality oflatch dogs 31 which extend radially outward from a correspondingplurality of openings 32 at the lower end 33 of the tubular sleeve 11.The latch dogs 21 engage an annular groove 34 at the top 14 of thepolished bore 15. The latch dogs 31 are held in a radially extendingposition by a latch dog housing 35, positioned adjacent the lower end 33of the tubular sleeve 11 in the annular space 13 between the tubularsleeve 11 and the setting tool 12. The latch dog housing 35 is axiallymoveable therein from a first downhole position, shown in FIG. 2a, inwhich the latch dogs 31 are supported in the extended position, to anuphole position, shown in FIG. 2b, wherein the latch dogs 31 arepermitted to retract from the annular groove 34. Once the latch dogs 31retract, the lower end 33 of the tubular sleeve 11 is released from thepolished bore 15.

[0027] In the downhole position, as shown in FIG. 2a, the latch doghousing 35 extends below the lower end 33 of the tubular sleeve 11 intothe annular space 16 between the setting tool 12 and the polished bore15. The latch dog housing 25 is releasably retained in the downholeposition by at least one shear screw 36 connected between the tubularsleeve 11 and the latch dog housing 25. A plurality of shear screws 36may be used to adjust a retrieval force required to release the latchdog housing 35.

[0028] As shown in FIG. 2b, the setting tool 12 is-lifted for retrievalfrom the wellbore and engages the latch dog housing 25 to move the latchdog housing 25 to the uphole position. An uphole facing shoulder 40,preferably adjacent a bottom end (not shown) of the setting tool 12mates with a downhole facing shoulder 41 at a bottom end 42 of the latchdog housing 25. Lifting pressure is applied to the setting tool 12 andthrough the shoulder 40 to the latch dog housing 25, sufficient toovercome the shear screws 36. The latch dog housing 25 moves axially tothe uphole position permitting the latch dogs 21 to retract into anannular groove 43 on the latch dog housing 25, releasing the latchingmechanism 30 and the debris screen 10 from the top of the polished bore15. The setting tool and debris screen 10 are then retrieved to surfaceafter setting a packer (not shown) if included in the liner hangerassembly string.

[0029] Preferably, a plurality of slots or ports 39 are formed at thebottom end 42 of the latch dog housing 25 as the means provided topermit the fluid flow A to and from the wellbore, through the sleeveannulus 13 and the tool annulus 16.

[0030] In a second embodiment of the invention, as shown in FIGS. 3a-3 band 4 a-4 b, the latching mechanism 30 is a collet system 50,particularly well suited to smaller diameter tools having a smallertolerance between the setting tool 12 and the polished bore 15. Thepolished bore 15 or tieback receptacle is the same as set forth in theprevious embodiment in FIGS. 2a-2 b.

[0031] A plurality of downwardly depending collet fingers 51, are formedadjacent the lower end 33 of the tubular sleeve 11. The collet fingers51 engage the same form of annular groove 34, as shown in FIG. 3b at thetop 14 of the polished bore 15.

[0032] As shown in FIG. 4a, a collet retainer 52 is positioned in theannular space 13 between the tubular sleeve 11 and the setting tool 12and is releasably connected to the tubular sleeve 11 in a downholeposition for supporting the collet fingers 51 in an engaged position inthe annular groove 34 at the top 14 of the polished bore 15. Withreference to FIG. 4b, the collet retainer 52 is axially moveable forenabling alternate support and release of the collet fingers 51. Aprofiled outer surface 56, at the lower end 55 of the collet retainer52, permits the collet fingers 51 to be moved out of the annular groove34. Once the collet fingers 51 are released, the tubular sleeve 11 canbe removed from the polished bore 15.

[0033] As shown in FIG. 4a, the collet retainer 52, in the downholeposition, extends below the lower end 33 of the tubular sleeve 11 intothe annular space 16 between the setting tool 12 and the polished bore15. The collet retainer 52 is releasably retained in the downholeposition by at least one shear screw 53 connected between the tubularsleeve 11 and the collet retainer 52. A plurality of shear screws 53 maybe used to adjust a retrieval force required to release the colletretainer 52.

[0034] Best seen in FIG. 3b, a plurality of ports 54 are formed at abottom end 55 of the collet retainer 52 for permitting the flow A offluids therethrough.

[0035] As shown in FIG. 4b, and described in the previous embodiment,the setting tool 12 is lifted for retrieval from the wellbore. Theuphole facing shoulder 40 adjacent the bottom end of the setting tool 12mates with a downhole facing shoulder 54 at a bottom end 55 of thecollet retainer 52. Lifting pressure is applied to the setting tool 12and through the shoulder 40, sufficient to overcome the shear screws 53.The collet retainer 52 moves axially to the uphole position permittingthe collet fingers 51 to retract into the profiled outer surface 56 ofthe collet retainer 52, releasing the debris screen 10 from the top ofthe polished bore 15. The setting tool and debris screen 10 are thenretrieved to surface after setting a packer (not shown) is included inthe liner hanger assembly string.

The Embodiments of the Invention in which an Exclusive Property OrPriviledge is Claimed are Defined as Follows:
 1. A debris screenpreventing the ingress of debris to a tool annulus between a settingtool inserted into a bore of a downhole tool in a wellbore, the settingtool being axially moveable within the bore, the debris screencomprising: a tubular sleeve positioned about an exterior surface of thesetting tool, and axially moveable thereon and defining a sleeve annulustherebetween, the sleeve having a plurality of ports formed therethroughfor permitting fluid communication between the sleeve annulus and thewellbore; a screen formed over the tubular sleeve for preventing thepassage of debris therethrough; a seal positioned at a top end of thetubular sleeve and extending between the tubular sleeve and the settingtool, the seal permitting limited fluid communication therethrough forpreventing pressure locking while blocking debris; and means forlatching the tubular sleeve sealingly to a top of the bore andpermitting fluid communication between the sleeve annulus and the toolannulus.
 2. The debris screen as described in claim 1 wherein the meansfor latching the tubular sleeve sealingly to the top of the borecomprises: a latching mechanism operable between the tubular sleeve andthe bore wherein the latching mechanism is adapted for releasablyengaging an annular groove at a top of the bore for retaining thetubular sleeve adjacent the top of the bore.
 3. The debris screen asdescribed in claim 2 wherein the latching mechanism further comprises: aplurality of latch dogs, extendable radially outward through a pluralityof corresponding openings at a lower end of the tubular sleeve, forengaging the annular groove at the top of the bore, the latch dogs beingmoveable between a radially extended position and a retracted position;a latch dog housing, positioned in the tool annulus and releasablyconnected to the tubular sleeve in a downhole position for supportingthe latch dogs in the extended position and being axially moveablethereupon to an uphole position following release from the tubularsleeve, to permit the latch dogs to move to the retracted positionthereby releasing the tubular sleeve from the bore; and ports formed inthe latch dog housing for permitting fluid communication between thesleeve annulus and the tool annulus.
 4. The debris screen as describedin claim 3 further comprising a downwardly depending shoulder at a lowerend of the latch dog housing wherein when the setting tool is lifted toexit the bore, the setting tool engages the shoulder and liftingpressure is applied to the latch dog housing sufficient to overcome thereleasable connection and move the latch dog housing to the upholeposition permitting the latch dogs to move to the retracted position andreleasing the tubular sleeve from the bore.
 5. The debris screen asdescribed in claim 4 wherein the latch dog housing is releasablyconnected to the tubular sleeve by at least one shear screw.
 6. Thedebris screen as described in claim 2 wherein the latching mechanismfurther comprises a collet system.
 7. The debris screen as described inclaim 6 wherein the collet system comprises: a plurality of downwardlydepending collet fingers, formed at a lower end of the tubular sleeve,for engaging the annular groove at the top of the bore; a colletretainer positioned in the tool annulus and releasably connected to thetubular sleeve in a downhole position for supporting the collet fingersin the annular groove at the top of the bore, the collet retainer beingaxially moveable thereupon to an uphole position following release fromthe tubular sleeve, to permit the collet fingers to be released from theannular groove thereby releasing the tubular sleeve from the bore; andports formed in the collet retainer for permitting fluid communicationbetween the sleeve annulus and the tool annulus.
 8. The debris screen asdescribed in claim 7 further comprising a downwardly depending shoulderat a lower end of the collet retainer wherein when the setting tool islifted to exit the bore, the setting tool engages the shoulder andlifting pressure is applied to the collet retainer sufficient toovercome the releasable connection and move the collet retainer to theuphole position, forcing the collet fingers out of the annular grooveand releasing the tubular sleeve from the bore.
 9. The debris screen asdescribed in claim 1 wherein the screen is a wedge wire screen.
 10. Thedebris screen as described in claim 3 wherein the screen is a wedge wirescreen.
 11. The debris screen as described in claim 8 wherein the screenis a wedge wire screen.
 12. The debris screen as described in claim 1wherein the downhole tool is a liner hanger assembly.
 13. The debrisscreen as described in claim 3 wherein the downhole tool is a linerhanger assembly.
 14. The debris screen as described in claim 8 whereinthe downhole tool is a liner hanger assembly.
 15. A debris screenpreventing the ingress of debris to an annulus between a setting toolinserted into a bore of a liner hanger assembly, the setting tool beingaxially moveable within the bore, the debris screen comprising: atubular sleeve positioned about an exterior surface of the setting tool,and axially moveable thereon and defining a sleeve annulus therebetween,the sleeve having a plurality of ports formed therethrough forpermitting fluid communication between the sleeve annulus and thewellbore; a screen formed over the tubular sleeve for preventing thepassage of debris therethrough; a seal positioned at a top end of thetubular sleeve and extending between the tubular sleeve and the settingtool, the seal permitting limited fluid communication therethrough forpreventing pressure locking while blocking debris; and means forlatching the tubular sleeve sealingly to a top of the bore andpermitting fluid communication between the sleeve annulus and the toolannulus.
 16. The debris screen as described in claim 15 wherein themeans for latching the tubular sleeve sealingly to the top of the boreis a latching mechanism operable between the tubular sleeve and the boreand wherein the latching mechanism is adapted for releasably engaging anannular groove at a top of the bore for retaining the tubular sleeveadjacent the top of the bore, the latching mechanism comprising: aplurality of latch dogs, extendable radially outward through a pluralityof corresponding openings at a lower end of the tubular sleeve, forengaging the annular groove at the top of the bore, the latch dogs beingmoveable between a radially extended position and a retracted position;a latch dog housing, positioned in the tool annulus and releasablyconnected to the tubular sleeve in a downhole position for supportingthe latch dogs in the extended position and being axially moveablethereupon to an uphole position following release from the tubularsleeve, to permit the latch dogs to move to the retracted positionthereby releasing the tubular sleeve from the bore: ports formed in thelatch dog housing for permitting fluid communication between the sleeveannulus and the tool annulus; and a downwardly depending shoulder at alower end of the latch dog housing wherein when the setting tool islifted to exit the bore, the setting tool engages the shoulder andlifting pressure is applied to the latch dog housing sufficient toovercome the releasable connection and move the latch dog housing to theuphole position permitting the latch dogs to move to the retractedposition and releasing the tubular sleeve from the bore.
 17. The debrisscreen as described in claim 16 wherein the latching mechanism is acollet system comprising: a plurality of downwardly depending colletfingers, formed at a lower end of the tubular sleeve, for engaging theannular groove at the top of the bore; a collet retainer positioned inthe tool annulus and releasably connected to the tubular sleeve in adownhole position for supporting the collet fingers in the annulargroove at the top of the bore, the collet retainer being axiallymoveable thereupon to an uphole position following release from thetubular sleeve, to permit the collet fingers to be released from theannular groove thereby releasing the tubular sleeve from the bore; andports formed in the collet retainer for permitting fluid communicationbetween the sleeve annulus and the tool annulus; and a downwardlydepending shoulder at a lower end of the collet retainer wherein whenthe setting tool is lifted to exit the bore, the setting tool engagesthe shoulder and lifting pressure is applied to the collet retainersufficient to overcome the releasable connection and move the colletretainer to the uphole position, forcing the collet fingers out of theannular groove and releasing the tubular sleeve from the bore.